This disclosure relates to additive manufacturing of aluminum articles.
Additive manufacturing technologies have been used and proposed for use for fabricating various types of articles from various types of materials. Broadly viewed, additive manufacturing can include any manufacturing process that incrementally adds material to an assembly during fabrication, and has been around in one form or another for many years. Modern additive manufacturing techniques, however, have been blended with three-dimensional computer imaging and modeling in various types to produce shapes and physical features on articles that are not readily produced with conventional molding, shaping, or machining techniques. Such techniques were initially developed using polymer compositions that are fusible or polymerizable in response to a controllable source of light or radiation such as a laser. Three-dimensional articles can be fabricated a layer at a time based on data from a corresponding layer of a three-dimensional computer model, which are generally as stereolithography. With these techniques, a polymer powder or polymerizable liquid polymer composition is exposed to a source of energy such as a laser to fuse a thermoplastic polymer powder by heating it to a fluid state or by initiating a reaction between components in a powder or polymerizable liquid composition. The powder or liquid can be applied a layer at a time by any known mechanism such as by spray or other application, but is often maintained in a bed where the article being fabricated is formed. After each layer is fused and solidified, the article is lowered in the bed or the level of the bed is raised so that a layer of powder or liquid covers the previously-formed layer of the article, and another layer of the powder or liquid is fused and solidified by selective exposure to the energy source based on data from another corresponding layer of the computer model.
Additive manufacturing techniques have also been used for the fabrication of metal articles. Metal thermal spray and other additive manufacturing techniques for metals have of course been known for some time. The application of stereolithographic manufacturing techniques to metals has led to significant advancements in the fabrication of three-dimensional metal articles. Using such techniques, a metal article being manufactured is maintained in a bed of metal powder, with the surface of the article below the surface of the powder in the bed so that there is a layer of metal powder over the surface of the article. Metal powder in this layer is selectively fused such as by selective exposure to an energy source such as a laser or electron beam, according to data from a corresponding layer of a three-dimensional computer model of the article. After each layer is fused and solidified, the article is lowered in the bed or the level of the bed is raised so that a layer of metal powder covers the previously-formed layer of the article, and another layer of the powder is fused and solidified by selective exposure to the energy source based on data from another corresponding layer of the computer model. The resulting can be relatively complex, compared to structures obtainable by conventional metal fabrication techniques such as casting, forging, and mechanical deformation.
Attempts to fabricate aluminum and aluminum alloy articles using additive manufacturing techniques have met with limited success. Aluminum alloys used for casting have been proposed or tried for powder casting or additive manufacturing. However, many such alloys have limitations on strength or other physical properties that renders them unsuitable for many applications, including but not limited to aerospace and other applications requiring strength. For example, the alloy AlSi10 Mg has been evaluated for additive manufacturing, but exhibits poor ductility and fracture toughness. High-strength aluminum alloys are also known. For example aluminum alloys 6061 and 7075 are well-known for their high strength in wrought aluminum articles. However, articles formed from these alloys using additive manufacturing techniques are susceptible to crack formation.